This invention relates to a surgically implantable neural prosthesis and more particularly to a prosthesis which may be inserted into the eye in a folded state and later expanded to its operating state for contracting neural tissue such as the retina.
Tremendous societal benefits will result if some vision can be restored to patients who have become blind as a result of retinal disease such as age-related macular degeneration and retinitis pigmentosa. Macular degeneration affects 700,000 additional Americans each year and is the leading cause of blindness in the Western world. Retinitis pigmentosa, while less common, is the leading cause of inherited blindness and affects 1.6 million people worldwide. Both conditions are degenerative diseases of the outer retina. Macular degeneration primarily affects individuals near retirement age, whereas retinitis pigmentosa primarily affects younger adults. Macular degeneration causes loss of the central part of the visual field, making reading impossible. Retinitis pigmentosa initially causes gradual loss of peripheral vision, followed by loss of central vision resulting in total blindness. No effective preventative or cure is known for either disease.
These two diseases both arise from the anatomical problem of rod and cone degeneration. That is, in both diseases the rods and cones at the back of the retina degenerate, leaving the retina insensitive to light. The patient often becomes blind despite the retina retaining an active connection to the brain through a functioning optic nerve.
In the eye, the rod and cone photoreceptors are located far below the surface of the retina, while the ganglion cells and axons leading to the brain exist at the front of the retina. The ganglion cell layer lies only 20-40 microns from the retinal surface, and it can easily be stimulated by small currents from microelectrodes placed against or near the front retinal surface. See, U.S. Pat. No. 5,597,381. A goal of the retinal prosthesis of the invention is to electrically stimulate the retinal neurons to convey at least the outlines of a visual scene transmitted to the prosthesis as by an infrared laser, radio frequency source or other wireless techniques from outside the eye. An initial goal is thus to restore sufficient vision to blind patients to allow them to walk down a street unaided.
The neural prosthesis according to the invention includes a foldable substrate with a least one electronic component supported by the substrate. At least one air channel is disposed within the substrate. The electronic component may include an integrated circuit and/or an electrode array for stimulating neural tissue such as retinal tissue. It is preferred that the foldable substrate in an expanded state provides close apposition between the electrode array and the neural tissue.
In a preferred embodiment, the substrate includes a central region surrounded by projecting structures, each of the projecting structures including a microchannel. Each of the projecting structures includes the electrode array for stimulating neural tissue and the central region comprises power, control and driving circuits. The central region may be made of semiconducting material and the projecting structures made of a flexible insulating polymer which may contain polyimide. It is also preferred that the central region include a micromachined semiconducting nib through which a compressed gas or fluid can flow into the channel in each of the projecting structures.
Because the neural prosthesis of the invention includes a foldable substrate, the prosthesis can be inserted, for example, into the eye in a folded state through a relatively small surgical opening and once inside, inflated to an unfolded state to stimulate a relatively large area of neural tissue such as the retina. The prosthesis of the invention will also provide sufficient semiconductor area to implement the power, control and driving functions necessary for its operation.